1. Field of the Disclosure
This disclosure relates to a liquid crystal display device with improved transmittance and contrast ratio, and a driving method thereof.
2. Description of the Related Art
As the information society grows, flat display devices capable of displaying information have been widely developed. These flat display devices include liquid crystal display (LCD) devices, organic electro-luminescence display (OLED) devices, plasma display devices, and field emission display devices. Among the above display devices, LCD devices have the advantages that they are light and small and can provide a low power drive and a full color scheme. Accordingly, LCD devices have been widely used for mobile phones, navigation systems, portable computers, televisions and so on.
LCD devices control the transmittance of a liquid crystal on a liquid crystal panel, thereby displaying a desired image. LCD devices generally have a poor viewing angle.
In order to improve the viewing angle, an LCD device with an in-plane switching (IPS) mode has been proposed which generates a horizontal electric field or an in-plane electric field by means of pixel electrode and common electrode arranged on the same substrate. Also, the pixel and common electrodes included in the LCD device of the IPS mode have been designed to be arranged in one of several configurations, including a one-matal-one-ITO (1-metal-1-ITO), a two-ITO (2-1TO), and a 2MoTi configuration.
Among these electrode arrangement configurations, the 1-metal-1-ITO configuration includes common electrodes 103a and 103b and a pixel electrode 107 arranged on different layers, as shown in FIG. 1. The common electrodes 103a and 103b, which include a metal film, are disposed on a substrate 101. Meanwhile, the pixel electrode 107, which includes a transparent conductive film such as an ITO film is disposed on a passivation (or protective) film 106.
The 1-metal-1-ITO configuration uses a mask in the formation of the common electrodes 103a and 103b. The mask can be aligned in an undesired position which is then shifted from a desired position to one direction (for example, to the right side of the desired position) during the formation of the common electrodes 103a and 103b. In other words, a mask misalignment can be generated. In this case, shifted common electrodes 105a and 105b may be formed. The shifted common electrodes 105a and 105b are separated in differing distances from the pixel electrode 107. More specifically, a first region A defined between the first shifted common electrode 105a and the pixel electrode 107 is of a width narrower than that of a second region B formed between the second shifted common electrode 105b and the pixel electrode 107. As such, the transmittances of the first and second regions A and B with regards to the same voltage are different from each other, thereby deteriorating the overall (or general) transmittance as shown in FIG. 2.
The 2-ITO configuration includes a pixel electrode 113 and a common electrode 115 arranged on the same layer, i.e., on the surface of a substrate 111, as shown in FIG. 3A. The pixel electrode 113 and the common electrode 115 are formed of the same material such as ITO.
In the 2-ITO configuration, an equipotential is formed on the pixel electrode 113 and the common electrode 115. As such, a mean efficiency of a liquid crystal positioned above the pixel electrode 113 and the common electrode 115 is decreased as shown in FIG. 3B. Likewise, the transmittance of the pixel region is lowered. Therefore, the contrast ratio is deteriorated.
Similarly, the 2MoTi configuration includes a pixel electrode 123 and a common electrode 125 arranged on the same layer, i.e., on a substrate 121, as shown in FIG. 4A. The pixel electrode 123 and the common electrode 125 are made of the same material such as MoTi.
As the pixel and common electrodes 123 and 125 made of MoTi are opaque, light can not penetrate through the pixel and common electrodes 123 and 125, as shown in FIG. 4B. In other words, the aperture of the pixel region is lowered. Accordingly, the light transmittance and brightness are deteriorated.